Add usage

README.md

@@ -1,3 +1,22 @@
 # mfeed
 
 very simple miniflux tool, expected for the tool to be piped to other programs.
+
+## Usage
+
+```
+$ mfeed
+examples:
+    mfeed create {category_id} {feed_url}
+
+usage: mfeed [-h] {feeds,categories,create} ...
+    feeds       list all the feeds you have
+    categories  list all the categories you have
+    create      create a new feed
+
+positional arguments:
+  {feeds, categories, create}
+
+options:
+  -h, --help  shows this help page
+```